ARM: sirf: move irq driver to drivers/irqchip

This updates the irqchip drier for prima2 to the current practices by
moving it into drivers/irqchip and integrating it into the irqchip_init
infrastructure. We also now use a linear irq domain as a preparation
for sparse IRQ suport.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Gleixner <tglx@linutronix.de>